Which sea creature has the largest eyes in the animal kingdom?

The colossal squid, with eyes around 27 centimetres across - roughly the size of a dinner plate, and several times larger than any other animal's, including whales far bigger than it is.

That disproportion needed explaining, and modelling published in 2012 provided the best answer: enormous eyes offer no advantage for spotting ordinary prey, but they do help with one specific task - detecting the faint glow of plankton disturbed by something very large moving through dark water, at ranges over a hundred metres. The eye is not for hunting. It is a sperm whale alarm, and sperm whales are the only animal that routinely eats them.

The animal itself was barely known until recently. It is heavier than the giant squid though shorter, lives in the Southern Ocean, and has swivelling hooks on its tentacles rather than only suckers - sperm whales are caught with circular scars that match them. A live colossal squid was filmed in its own habitat for the first time in 2025, a century after the species was described, and the specimen was a juvenile about thirty centimetres long.